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Finder Scope Location

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8 replies to this topic

#1 daviddecristoforo

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Posted 23 January 2019 - 12:03 PM

The scope I'm building will have both a Telrad finder and a "conventional" right angle finder scope. Almost every cope I've looked at has the finder(s) mounted on the "top" of the main tube. But if I mount the both Telrad and the right angle finder scope in that position, they could be awkwardly placed unless one has a neck like a giraffe!. So my thought is to mount the Telrad on top and have the right angle finder mounted under the focuser where it will be more easily accessible. Any thoughts on this?



#2 roscoe

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Posted 23 January 2019 - 12:17 PM

A possible problem with the finder mounted under is that the user's breath might steam up the finder EP when looking through the scope.

 

The finders on my 10" scope are mounted atop the tube, the focuser is at about 45 degrees. My red-dot is a rifle-type one, it mounts on a Picatinny rail system, so I made a wood rail for it to clamp on that is bolted to the rings that hold my finder.  I lean down, sight in with the red-dot, then stand back up, find the object in the right-angle finder, then move my eye a few inches to the main EP.  The whole assembly - finder and red-dot, is held to the scope tube with two bolts and knurled nuts, I remove it for transport and storage.



#3 daviddecristoforo

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Posted 23 January 2019 - 12:35 PM

So could the finder scope not be mounted a bit farther down the tube so that one is not breathing on the finder eyepiece when looking into the focuser?
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#4 Barlowbill

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Posted 23 January 2019 - 01:32 PM

The way my Orion 8" Dob is factory set-up, the finder scope is "above"  the focuser.  The finder's ep sits about 4" behind the focuser.  It is quite comfortable to view the finder ep them move to the focuser.  far enough away that breath at either position does not affect either eyepiece.  Go to Orion's web site and look at picture of a Dob with a Raci.



#5 jtsenghas

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Posted 23 January 2019 - 02:05 PM

So could the finder scope not be mounted a bit farther down the tube so that one is not breathing on the finder eyepiece when looking into the focuser?

That's what I'd recommend if you don't want the RACI between the focuser and the Telrad.  Since the Telrad can be used a significant distance behind it and requires you to sight parallel to the scope tube, I prefer to put the Telrad on top and as far up the tube as possible. My RACI is closer to me than the focuser and a bit further down, which helps both with fogging issues and balance, since it is that much closer to the altitude axis. This location has the added advantage at outreach events that I can sight through the finder and re-aim the scope when an observer is at the eyepiece without either of us getting in the way of the other.


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#6 hcf

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Posted 23 January 2019 - 02:16 PM

On my Dob, I found that with the RACI and the Telrad, the RACI gets used much more than the Telrad. The Telrad is used just to get to the ballpark and then the RACI takes over. Which is why I keep the RACI close and the Telrad further away. For the Telrad I used zip ties and tried various positions on the OTA, and ended up putting the Telrad beyond the RACI.

 

If I set up another Dob, I will probably go with a RDF, DIY mounted on top of the RACI.


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#7 Bill Kocken

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Posted 23 January 2019 - 06:07 PM

On my 16" dob I put the telrad around towards the top of the tube and the RACI is mounted around towards the bottom. The raci isn't really in the way of my breath. The bigger issue is that it causes balance problems. I have to add quite a bit of counterweights. 



#8 daviddecristoforo

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Posted 23 January 2019 - 06:34 PM

 ...The bigger issue is that it causes balance problems. I have to add quite a bit of counterweights. A

My thought was to mount the Telrad, RACI, and focuser and install the mirrors. Then find the COG and position the whole assembly on the mount. Then I’ll add a small sliding counterweight to compensate for the eyepiece weight.


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#9 Bob4BVM

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Posted 24 January 2019 - 02:03 AM

On my Dob, I found that with the RACI and the Telrad, the RACI gets used much more than the Telrad. The Telrad is used just to get to the ballpark and then the RACI takes over. Which is why I keep the RACI close and the Telrad further away. For the Telrad I used zip ties and tried various positions on the OTA, and ended up putting the Telrad beyond the RACI.

 

If I set up another Dob, I will probably go with a RDF, DIY mounted on top of the RACI.

After putting a RACI on my Dob, I eventually removed the telrad cause I rarely used it. The RACI is so much easier to sight thru than having to crane my neck to see the telrad rings, plus it dewed up a lot more than the raci.

 

I like the idea above of mounting a finder low on the tube so you can easily use in outreach. I sometimes put two finders in my scope just for that reason !

 

These days I am perfectly happy with a 70mm RACI & a green laser combo on the Dob. I can very quickly point to a region and then actually see many targets in the raci.  Probably will do similar for the binoscope until I get the DSCs running.

 

CS

Bob


Edited by Bob4BVM, 24 January 2019 - 02:04 AM.

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